The conventional installation of piping and conduitry by means of threaded or cemented joinder is well-known. These techniques require substantial preparation and installation time, which often is justified. There are, however, many applications where if economy of labor and material cost are of serious concern, these techniques are not acceptable.
The thermal joinder of pipes made of thermoplastic resin has been adopted as a solution to the above problem for installation in which labor cost and cost of materials are of substantial importance. The householder who is installing garden sprinklers will not find this invention attractive to him, because the total cost of material is relatively small, and unit savings will as to him be inconsequential. Also, he has all day to do the job. In contrast, a contractor installing large arrays of piping finds that even marginal savings in time and material mount up to substantial cash.
The installer of presently-known thermally installed piping join abutting pipe sections with a heat coil between them. The coil is connected to a current source that generates heat to soften and locally melt the plastic material. At the same time a peripheral clamp is tightened onto the outside of the joinder to press the outer member onto the inner member. The members fuse together, and when they cool the joinder is unitary, with the coil left embedded.
By then the installer has faced several problems. For one, two electrical leads emerge from the assembly to be connected to the current source. It is troublesome and sometimes not possible to arrange for them to emerge where they are readily accessible to the installer. Then he must reach around for the leads, and especially on larger sizes, they may be too short conveniently to be connected to the current source. Whatever the situation, it requires that he bother with it, and this takes time, which costs money.
In addition, a compressive force must be exerted on the joinder so the two bodies are pressed together. Otherwise an incomplete joinder might be made. The conventional means to accomplish this is by way of a commond circular hose clamp tightened by a screw. The problem this presents is that once it is tightened, there is no follow-up as the consequence of changing circumstances unless the man stands there and does it. When the substrate material melts, the compressive forces are relieved. Then one must either assume that there will be enough residual compression from the forces that were first applied, or the installer must continually re-tighten the clamp.
Neither of these arrangements is optimal. There is a latent uncertainty in depending on a previously applied force after part of the substrate has softened or melted. The need to periodically tighten the clamp is costly.
This invention should be regarded in the context that a substantial number of these joinders are usually being set at once. It is a considerable advantage for the installer to preassemble a group of these joinders and then merely to move from one to the next to apply the necessary current. Thereafter he can leave the joinder unattended, the clamp of this invention exerting a prevailing compression while the joinder fuses and cools.
Even more conveniently, this invention enables the installer to reduce the complexities and time consumed by making it possible for all joinders of any size to consume the same length of time in the heating cycle, rather than to require longer times for larger sizes than for smaller sizes.